Once the seedlings reach 2" tall, thin the plants with scissors to one plant per pot.
The main difference between summer and winter squash is that winter squashes have hard, thick rinds that will help them store for long periods of time. In cooler regions, you can start plants indoors three weeks before the last frost date. You don't want to start plants any earlier than this because older plants sometimes will not transplant well.
To start the winter squash indoors, put two seeds, 1" deep into 4" peat pots and water them until the soil was moist (Image 1). For best germination, you need to maintain the seeds at a constant temperature of 65 to 85 degrees Fahrenheit. Using grow lights is the best way to maintain a constant temperature.
Once the seedlings reach 2" tall, use scissors to thin the plants to one per pot. Also, before you plant the seedlings outdoors, harden off the seedlings. Hardening off means to gradually acclimate the seedlings to the outdoors. Place seedlings outside during the day under shrubs or trees when the temperatures are above 40 degrees Fahrenheit. Don't forget to bring the seedlings in at night and after five to seven days of hardening off, they will be ready for transplanting outside (Image 2).
Winter squash needs a sunny, open site for three months or more of frost-free growing time. They require plenty of room for their long, wandering vines. Squash likes a soil that is rich in organic matter, both for nutrients and a good supply of moisture.
To grow a planting of winter squash the soil should be fertilized with a 10-10-10 formula, meaning there are added amendments of 10 percent of each need element — nitrogen, phosphorus and potassium. Using a garden fork you turn the fertilizer into the soil at least 12" deep. Next, insert a soil thermometer into the ground to make certain the temperature is at least 70 degrees Fahrenheit.
To transplant seedlings, you dig a hole to the same depth as the peat pots. Set four seedlings, pot and all, in hills on the raised beds about 3' apart. Try not to crush the peat pots so you don't disturb the plant roots as you transplant the seedlings. Pack soil around the seedlings and then lightly water the plants. Also be sure the plants are placed in the hills side by side instead of one long row. This process will help the pollination of the flowers and the fruiting as the pollen passes from flower to flower (Image 1).
Once the seedlings have been up about one week, be sure to thin to the two strongest plants per hill. Crowded plants produce less fruit and are more likely to develop diseases. If there is a danger of disturbing the other seedlings, just pinch off the extras instead of pulling them out. For large deep-rooted plants, you can use scissors or bypass pruning shears to cut the stems off at the soil line (Image 2).